A magnetic memory cell includes a non-magnetic layer sandwiched by magnetic layers in which information is stored as directions of magnetic vectors. This type of the memory cell employs the giant magnetoresistive (GMR) effect which allows magnetic vectors to quickly switch the directions in the magnetic layer by an application of an external magnetic field. When magnetic vectors in both magnetic layers have the same direction, which is called a "Parallel", the magnetic resistance indicates a minimum value over the memory cell while the memory cell shows the maximum value in an opposite direction, which is called an "Antiparallel." Since the external magnetic field alters the direction of magnetic vectors and the magnetoresistive value according to the direction, the GMR effect is applied to a sensor as well as a memory.
The memory cell, for example, has pinned and free magnetic layers separated by an insulation or barrier layer. The magnetic vectors in the pinned magnetic layer are pinned by an anti-ferromagnetic layer placed adjacent the pinned magnetic layer and ones in the free magnetic layer are switched by an external magnetic field. A very thin insulation layer forms a tunneling junction between the pinned and free magnetic layers. In order to sense states in the memory cell, a constant current is applied through the memory cell. As the magnetic resistance varies according to the state stored in the cell, the voltage is sensed over the memory cell. To write or change the state in the memory cell, the external magnetic field is applied that is sufficient to completely switch the direction of the magnetic vectors of the free magnetic layer.
The memory cell memorizes one bit information. As a computer system processes much more information to handle complexes tasks, a memory device with much higher speed and density is needed to improve the performance of the computer system.
Accordingly, it is a purpose of the present invention to provide an improved MRAM device having a high density memory capacity.
It is another purpose of the present invention to provide an improved MRAM device having a high speed operation.
It is still another purpose of the present invention to provide an improved MRAM device having a low power consumption.